[time-nuts] Linear voltage regulator hints...
magnus at rubidium.dyndns.org
Wed Dec 10 19:46:10 EST 2014
On 12/10/2014 12:57 AM, Richard (Rick) Karlquist wrote:
> On 12/9/2014 3:02 PM, Bob Camp wrote:
> Here's an overnight ADEV plot against the new Cs of where we are in
> the project. Red is ADEV. Green is the TIC. Blue is the output of the
> GPSDO to Channel A and the Cs to Channel B of my 5335A measuring TI,
> using the 1PPS from my GPSDO to trigger the external gate. I see that
> the Cs phase has drifted down slightly vs my GPSDOe. I wonder if this
> is an indication of a calibration problem with the Cs or some subtle
> issue on my board?
>> Looks perfectly normal to me. Your Cs is sensitive to magnetic field.
>> Have you “zeroed” it out? No of course not, nobody does. (almost
>> nobody …).
> This reminds me of the great CBT demagnetizer debate at HP.
> Even Len Cutler didn't think this was necessary, at least
> in the 5071, and possibly the 5061. When Len says something
> is overkill, you can be sure of it. Anyway, we still had
> to support a CBT demagnetizer for customers who wanted it.
> The customer (with money to spend) is always right. The
> 5071 measures the C-field with a Zeeman line measurement
> and adjusts it if necessary.
The C-field coil and it's main magnetization should be servoed like that
for a modern Cesium. The possible problem lies if the magnetization
causes a large enough gradient along the beampath, but it would have to
be pretty strong to make any significant impact, considering the mymetal
shields and other materials involved, so Len is naturally right.
I have yet had a good reason to use my CBT degausser.
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